This application relates to magnetic disc drives and more particularly to an improved disc drive clamp and disc drive spindle motor apparatus for centering and mounting an information storage disc within the disc drive.
Disc drives are data storage devices that store digital data in magnetic form on a storage medium on a rotating information storage disc. Modern disc drives include one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g., a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate locating of the head over the center of the desired track.
The heads are mounted via flexures at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs.
Spindle motor assemblies often utilize a rotating spindle hub journaled to a non-rotatable spindle shaft. A disc clamp is typically secured to the rotating spindle hub to exert a downward axial force on the mounted information storage discs and disc spacers in order to securely fasten the discs and spacer together on the hub. Typically, the disc clamp is basically an annular leaf spring that is sized such that its outer rim exerts the downward force through a series of equally spaced screws positioned around the central portion of the clamp and torqued through holes in a central portion of the clamp into the spindle hub. The spaced radial positioning of the screws is beneficial for exerting a distributed clamping force on the stacked discs on the spindle assembly because the force is exerted at the periphery of the clamp in closer proximity to the mounted information storage discs and disc spacers. However, the screw is a discrete source of the clamping force, thus the distribution of the downward force around the periphery of the clamp, against the adjacent disc is exerted in a non-uniform manner. Non-uniform clamping force can generally cause variations in the load force applied and, as a result, can cause the top mounted information storage disc to be physically distorted. Distortion of the top disc, even by as little as 100 micro inches, can lead to generation of unacceptable operational errors during recording and reproduction of data on the information storage disc.
In a second type of spindle motor assembly the spindle shaft and spindle hub portion both rotate about a bearing sleeve. Here, a single screw can be used to secure the disc clamp to the rotating spindle shaft because the shaft rotates with the screw (as opposed to the non-rotatable shaft where a plurality of screws must be positioned in the hub about the shaft). However, in order to develop a clamping force with a single screw similar to the force developed by the plurality of screws surrounding the non-rotatable shaft, it is necessary to apply a much higher torque to the single screw. This relatively high torque requirement can lead to a number of problems including over-stressing the spindle shaft bearing, stripping threads, and the generation of particles during the torquing process. These high-torque related problems can damage the bearing and lead to failure of the spindle motor.
Currently, there is a need in the relevant art to overcome the shortcomings of the traditional single screw disc drive spindle motor assembly, as well as the non-rotatable multiple screw spindle shaft spindle motor. Furthermore, most current designs do not use the disc clamp to center the disc during installation. The centering of the disc is critical to the accurate locating of the head over the center of the desired track. Most centering occurs through the use of additional structures and operations, which can be complex and costly. Therefore, there is also currently a need in the relevant art to overcome the shortcomings of the traditional centering structures and operations for centering a disc on a drive spindle motor assembly.
Against this backdrop the present invention has been developed. The present invention is an apparatus and method for uniformly centering and retaining an information storage disc on a spindle motor.
In accordance with one preferred embodiment, the invention can be implemented as a disc drive spindle motor assembly including a rotatable motor spindle having a top portion and a hub portion, and an annular disc mounted over the top portion and supported on the hub portion. The assembly further includes an annular disc clamp mounted over the top portion of the spindle, and having a centering portion and a peripheral clamping portion. A disc clamp retainer is fastened to the spindle applying a compressive force to the disc clamp to secure the disc against the hub portion. The centering portion of the disc clamp has a series of spaced centering tabs adapted to abut the spindle and symmetrically push against the annular disc when the compressive force is applied to the disc clamp.
The invention can be implemented in accordance with another preferred embodiment as a disc clamp for use in centering and attaching an information storage disc to a disc drive spindle motor assembly having a spindle. The disc clamp includes an annular disc shaped body having a centering portion around a central aperture and an annular peripheral clamping portion. The centering portion has a series of centering tabs extending inwardly toward the central aperture from the peripheral clamping portion. Each of the centering tabs have a middle portion, an inward surface for contacting the drive motor spindle, and an outwardly projecting tip surface for contacting the data storage disc. When the disc and the clamp are installed on the top portion of the spindle and a compressive force is applied to the middle portion of the clamp, the clamp acts to center the disc about the spindle, and clamp the disc to the hub portion of the spindle.
In some embodiments, a separate retainer member is used to maintain the clamp on the spindle. In some other embodiments the disc clamp includes a series of inwardly directed retainer tabs that engage the spindle to fasten the clamp about the spindle.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.